The advantages of continuous spinal anesthesia have long been appreciated by anesthesiologists. Unlike conventional single-shot techniques, continuous spinal anesthesia (“CSA”) with an indwelling catheter allows anesthesia of unlimited duration and the ability to carefully control the level of the block by administering repeated small, incremental doses of anesthetic. As compared to continuous epidural anesthesia, which has become widely used as a substitute for spinal, CSA generally requires far less drug to achieve the desired effect, has a definite endpoint of correct catheter placement, requires no “test dose,” and produces a much more reliable, less spotty block.
Unfortunately, technical problems have severely limited the usefulness of continuous spinal techniques. Until recently, the standard technique of inserting the spinal catheter through the spinal needle, coupled with the difficulty of manufacturing truly small needles and catheters, has meant large needles and catheters were required, resulting in an unacceptably high incidence of post-dural puncture headaches (“PDPH”).
In the mid 1980's, various advances fueled renewed interest in spinal anesthesia in general and in CSA in particular. Improvements in manufacturing ever-smaller conventional (QUINCKE.™) spinal needles of 25 gauge, 26 gauge, and even 30 gauge significantly reduced PDPH incidence. These results allowed for the use of spinal anesthesia in age groups and procedures not previously considered suitable.
At the same time, advances in catheter manufacture made possible spinal catheters of 28 gauge and 322 gauge which would fit through relatively small spinal needles. Unfortunately, these catheters proved difficult to handle, difficult to make, expensive, and, more ominously, associated with several reports of neurologic damage (i.e., cauda equina syndrome). Many clinicians therefore tried and abandoned them, and they were ultimately removed from the market by the Food and Drug Administration (“FDA”).
The FDA's decision to recall and ban the marketing of microspinal catheters for CSA in the U.S., and its requirement that any new device for CSA be subjected to an extremely stringent pre-market approval process, has resulted in a freeze on the development of these products, at least in the United States. Nevertheless, the injection of local anesthetics for the establishment of surgical anesthesia is not the only use to which such devices might beneficially be put. In fact, the injection of narcotics, such as FENTANYL.™, for analgesia of labor would be a very desirable use of such catheters.
Installing a conventional catheter generally requires various cumbersome steps involving threading long, very thin catheters through a spinal needle. Simply threading a catheter into the end of a spinal needle can be so difficult that some manufacturers include a “threading aid” as part of their kit. Once threaded, a degree of uncertainty exists for the clinician about how far to insert the catheter. Also, a risk exists that a piece of the catheter might be sheared off by the needle if the catheter were to be pulled back during the threading operation. In such case, bits of catheter could potentially be left behind in the intrathecal space. Furthermore, removing the spinal needle while holding the catheter in position can be a challenge. Additionally, attaching a hub/injection adapter to the naked end of the 28 g or 32 g catheter can be even more of a challenge. Finally, once the adapter is successfully attached, the small lumen of the catheter permits only a slow flow of either CSF or anesthetic. In short, the conventional spinal catheter threading operation requires considerable time and effort on the part of a clinician.
A parallel technical development has been the introduction of non-cutting spinal needles, such as the “Pencil Point” type needles, which have been shown to drastically reduce PDPH incidence. Examples of Pencil Point type needles include the Sprotte and Whitacre non-cutting spinal needles. In terms of PDPH incidence, a 22 gauge Sprotte seems to be roughly equivalent to a 25 gauge or 26 gauge Quincke, while a 24 gauge Sprotte or 25 gauge Whitacre essentially eliminates the risk of PDPH.
One problem of Sprotte and Whitacre non-cutting spinal needles is that the injection orifice is on the side of the needle. Failures of spinal anesthesia have been described as when the needle was “half-in, half-out” of the intrathecal space. Another problem with Sprotte and Whitacre spinal needles is that the smooth curved tip profile provides no definitive feedback signal or “click” when the dura is punctured. Such lack of feedback contributes to uncertainty of catheter tip placement.
One solution overcoming the limitations of the conventional catheters mentioned above and approved by the FDA is a flexible spinal needle described in U.S. patent application Ser. No. 10/694,235, filed Oct. 27, 2003, (U.S. 2005-0090801 A1, published Apr. 28, 2005) the disclosure of which is incorporated by this reference in its entirety herein. Specifically, the flexible spinal needle may be used for CSA while essentially eliminating the risk of PDPH.